With the introduction of cellular telephone networks, the mobile telecommunications industry has exploded in the last ten years. As a result, neither range nor economic considerations presently raise substantial barriers to mobile telephone use. By conservative estimate, there are now sixteen million cellular telephone subscribers in more than eighty countries. These subscribers represent but a fraction of the potential mobile telephone market. In fact, the number is expected to increase threefold to fifty-three million by 1996.
While the United States currently accounts for almost fifty percent of the world's cellular subscribers (Europe accounts for approximately twenty eight percent) it is believed that by 1996, thirty-five percent of the world's subscribers will be using a digital system.
Analog cellular networks will continue to provide competition as will wireless (cordless) telephones. The latter is expected to exceed fifty-eight million users by the year 2000. Telepoint applications have similarly been adopted around the world and cordless voice and data transmissions have become a reality with the development of the Wireless Private Branch Exchange (WPBX) and cordless local area networks (CLANs).
Against this background, communications engineers have now turned their attention toward the design, development and implementation of user-friendly and ergonomically disposed mobile telephones. For example, see U.S. Pat. Nos. 4,706,273 and 4,870,676, issued to Spear et al and Lewo, respectively, which are directed to vehicle sun visor telephones. See also, U.S. Pat. No. 4,905,270 which is directed to a vehicular hands-free telephone system.
As those skilled in the art will recognize, conventional mobile telephones generally present all information entry keys for all telephone functions. Such keys are adapted for use in cooperation with a single visual display--regardless of whether the functions are relevant in the current context of the communication. Moreover, such visual displays do not present sufficient information to prevent users from entering an irrelevant or improper key. As a result, an erroneous key selection results in either an error message or similar indication that an invalid key has been entered--neither of which is desirable from a user standpoint. To implement additional functions, conventional mobile telephones have incorporated additional keys which again correspond to functions which are neither relevant nor operable in all contexts. As a result, the size as well as the complexity of such handsets has been correspondingly increased.
In an effort to minimize the number of entry keys while increasing the number available features, mobile telephone designers have thus incorporated entry keys which may be used to initiate multiple functions. In some applications, &lt;shift&gt; keys have also been utilized. These multi-function entry keys have been designed to provide specific functions which are tied to particular communication contexts. This correspondence, however, is neither readily apparent nor logically referenced. For example, many cellular telephones utilize an entry key labeled &lt;send&gt; for use in both answering an incoming call as well as to originate an outgoing call. Similarly, many vehicular cellular phones utilize a &lt;control&gt; entry key which may be used to store selected telephone numbers, lock the handset, control the volume of the received communication and perform other selected operations. The syntax of these operations is also neither apparent nor consistent. For example, in conventional mobile telephones, storing a telephone number generally requires a three-step process, i.e., initiation of a store sequence, identification of a telephone number sought to be stored, and selection of a storage location. These steps and their sequence vary widely from manufacturer to manufacturer and from handset to handset. Most importantly, however, little if any on-line help--other than an error message--is provided to guide the user through the required syntax.
Applicants are aware of existing mobile and desk top telephones presently marketed which utilize three or more classes of signaling keys or "buttons" in combination with a single visual display. See, for example, Finnish Nokia 101 portable telephone which includes a first class of dual tone multi frequency (DTMF) keys, a second class of action keys, i.e., &lt;SEND&gt; and &lt;END&gt; and a third class of function keys, i.e., &lt;POWER&gt;, &lt;CLR&gt;, &lt;RCL&gt;, &lt;ALPHA&gt;, &lt;MENU&gt; and &lt;STO&gt;. Also included in this third class of keys is a browse button &lt;.uparw..dwnarw.&gt; for menu scanning. Similarly, Isotec Desktop Telephone Model No. 228 includes a first class of DTMF buttons, a second class of function buttons, i.e., &lt;TR/CON&gt;, &lt;HOLD&gt;, &lt;HF&gt;, &lt;VOL.uparw.&gt; and &lt;VOL.dwnarw.&gt;, etc. and a third class of specific soft-label buttons for use in initiating modem connections.